Article 1 section 2 never explicitly mentions slavery. Article 4 section 2 is talking about fugitives on the run, free states were not obligated to return freed slaves until The Fugitive Slave Act of 1850. The right to own slaves was never guaranteed by the constitution, the Supreme Court absolutely had the authority to interpret whether or not slavery was legal, and they did just that in Dred Scott V. Sandford

“Persons of African descent cannot be and were never intended to be citizens under the US Constitution.”

The founding fathers were very careful to never explicitly mention slavery because many of them viewed it as immoral and wrong.